1. Field of the Invention
The invention relates to the catheter for mechanically fragmenting clots within the vascular system and, in particular, within occluded synthetic vascular grafts. The catheter is used percutaneously thereby obviating invasive surgical procedures. The use of the catheter reduces or eliminates the need for pharmacological clot dissolution.
2. Background Information
Approximately 150,000 patients in the United States are undergoing chronic hemodialysis. A significant problem for these patients is thrombosis of their dialysis access grafts. This contributes greatly to patient morbidity and hospitalization. Various prior art techniques have attempted to break up clots and/or other obstructing materials, such as neo-intimal hyperplasia in the vascular system and in synthetic grafts. Although surgery has been the traditional management for thrombosed access grafts and fistulae, percutaneous chemical thrombolysis, the use of thrombolytic agents to dissolve clots, is playing an increasingly important role for hemodialysis patients. Currently, the most popular technique is pulse-spray thrombolysis; however, use of thrombolytic agents such as Urokinase or Streptokinase is associated with relatively high costs, prolonged procedure time, and the potential for bleeding complications. Chronic hemodialysis patients experience blockage of the synthetic access graft (the dialysis fistula) approximately 3–4 times a year. Use of thrombolytic agents requires the patient to spend a day in the hospital each time the dialysis fistula occludes. Moreover, pharmacological therapy requires long time commitments for infusion or medical personnel commitments for pulse-spray techniques.
Surgical thrombectomy has also been used to restore access for dialysis and has opened vascular ducts occluded by clots. Again, the expense is excessive because operating room time must be used. Such techniques use a Fogarty balloon catheter in the operating room, although a Fogarty balloon catheter may be used percutaneously.
Various mechanical devices have been developed that are designed to mechanically remove atheromatous plaque; most of these devices are said to remove thrombus material also. Most of these devices cut the material and then collect or remove the resulting debris from the vascular system. Various atherectomy devices are described in the following patents: U.S. Pat. No. 4,957,482 issued to Samuel Shiber; U.S. Pat. No. 4,696,677 issued to Halmut Masch; U.S. Pat. No. 5,034,001 issued to Michi E. Garrison et al.; U.S. Pat. No. 4,950,277 issued to Andrew Farr; U.S. Pat. No. 4,926,858 issued to Hanson Grifford, III, et al.; U.S. Pat. No. 4,886,061 issued to Robert E. Fischell et al.; U.S. Pat. Nos. 4,923,462 and 4,936,845, issued to Robert Stevers et al; and U.S. Pat. No. 4,909,781 issued to Royce Hosted. The above devices share common problems—they require larger sheath size and create a limited channel size. Moreover, the prior art devices do not automatically accommodate to changes in the inner lumen dimensions of the graft or vessel caused by the presence of a thrombus or automatically expand outward toward the vessel or conduit walls as the thrombus is being fragmented.
U.S. Pat. No. 5,030,201 issued to Aubrey Palestrant, typifies the problems associated with prior art mechanical devices. Palestrant teaches a plurality of parallel cutting blades which are contained during transport within a protective sheath. In operation, the device cuts a portion of the obstructing material and then a second means is used to manually expand the parallel cutting blade so that a larger core can be cut in the obstructing material. The Palestrant device relies on the relative movement of coaxial catheters to bow the blades outward. The amount of expansion is totally controlled by the operator and the Palestrant device cannot automatically compensate for changes in the inner lumen as obstructing material is removed. The coaxial structure also requires a large diameter protective sheath.
Various mechanical devices, rather than using rotating members to cut the obstructive material use ureteric stone catcher baskets mounted on a catheter tip to grab and remove thrombotic material. The following articles teach the use of such baskets to grab and remove thrombus: 1) “A Combined Technique for Peripheral Arterial Embolectomy” Arch Surg/Vol. 105, December, 1972; 2) “Removal of an iatrogenic foreign body from the aorta by means of ureteric stone catheter” Am. Heart J. March, 1967; 3) “Nonsurgical Techniques for Removal of Catheter Fragments From the Pulmonary Artery” Catheterization and Cardiovascular Diagnosis 9:109–112 (1983); 4) “Atraumatic retrieval of catheter fragments from the central circulation in children” European Journal of Cardiology, 1974, 1/4, 421–422; 5) “Removal of Intravascular Foreign Body with Stone Retriever” Urology, February 1981, Vol. XVII, No. 2; 6) “Retrograde Embolectomy” The Lancet, Apr. 6, 1963; 7) “Mechanical Clot Dissolution: New Concept” Radiology, April 1989, 17/:231–233; 8) “Mini basket for Percutaneous Embolectomy and Filter Protection Against Distal Embolization: Technical Note” Cardiovasc Intervent Radial (1991) 14:195–198; and 9) “Percutaneous Aspiration Thromboembolectomy” Radiology July, 1985; 156:61–66.
An article appearing in Radiology entitled “New Device for Percutaneous Fragmentation of Pulmonary Emboli” (Radiology, 1991; 180:135–137) combines a spinning impeller contained within a stone basket. The stone basket does not rotate and is necessary to center the rotating impeller so that it does not inadvertently cut the vessel wall. The device cannot automatically expand the mechanical fragmentor to accommodate the inner lumen dimensions of the vascular conduit.